I think comparatively, China & Korea suffered more during
the WWII under the ruthless Japanese. Hence, its understandable
that they feel outraged for symbolic act of Japanese PM visiting
the shrine, especially those class A war criminals caused the
greatest astrocities in the war.
Moreover, over the years, the Japanese did not really recognise the
brutalities they committed during the war, at least not the head
hunchos unlike the Germans, who have faced history
differently.
of course, there are other issues that complicate the situation -
like ownership of offshore islands, etc. And China gonna voice out
to cement their place as the big brother of this region...
By visiting the shrine, the Japanese are symbolising that they
"honor" those war mongers and have scant taint of regret or
learning from their lessons.
However, in light of economic benefits, this will blow over,
moreover its his last visit as capacity of PM liaoz, might as well
antagonise the Chinese and Koreans once more.